-1x2 +7x +18 = 0
ax2 bx c = 0
a = -1
b = 7
c = 18
Δ = b2-4ac
Δ = 7² - (4 * -1 * 18)
Δ = 49 - (4*-18)
Δ = 49 - (-72)
Δ = 121 Δ > 0
-x2+7x+18=0
x = -b ∓ √Δ 2a
x' = -7 - √121 2*-1 = -7 - 11.0 -2 = -18.0 -2 = 9.0
x" = -7 + √121 2*-1 = -7 + 11.0 -2 = 4.0 -2 = -2.0
x' = 9.0
x" = -2.0
S = {x ∈ R / x' = 9.0, x" = -2.0 }